JP6011586B2 - Method for producing grain-oriented electrical steel sheet - Google Patents

Description

  The present invention relates to a method for producing a grain-oriented electrical steel sheet having excellent magnetic characteristics, which can obtain a grain-oriented electrical steel sheet having excellent magnetic characteristics at low cost.

  A grain-oriented electrical steel sheet is a soft magnetic material used as a core material for transformers and generators, and has a crystal structure in which the <001> orientation, which is the easy axis of iron, is highly aligned in the rolling direction of the steel sheet. . Such a texture preferentially grows crystal grains with a (110) [001] orientation, which is referred to as a so-called Goss orientation, during secondary recrystallization annealing during the production process of grain-oriented electrical steel sheets. Formed through secondary recrystallization.

  Conventionally, such grain-oriented electrical steel sheets are heated to 1300 ° C. or higher by heating a slab containing Si of 4.5 mass% or less and an inhibitor component such as MnS, MnSe, AlN, etc., to temporarily dissolve the inhibitor component. After that, after hot rolling and performing hot-rolled sheet annealing as necessary, the final sheet thickness is obtained by cold rolling at least once with one or two intermediate sandwiches, followed by primary recrystallization in a wet hydrogen atmosphere. After annealing, primary recrystallization and decarburization are performed, and then an annealing separator mainly composed of magnesia (MgO) is applied, and then secondary recrystallization and inhibitor components are purified at 1200 ° C. for about 5 hours. It has been manufactured by performing final finish annealing (for example, Patent Document 1, Patent Document 2, and Patent Document 3).

  As described above, when manufacturing conventional grain-oriented electrical steel sheets, precipitates (inhibitor components) such as MnS, MnSe, and AlN are included in the slab stage, and these inhibitor components are added by high-temperature slab heating exceeding 1300 ° C. A process of causing secondary recrystallization by once forming a solid solution and finely precipitating in a subsequent process has been adopted. As described above, in the manufacturing process of conventional grain-oriented electrical steel sheets, slab heating at a high temperature exceeding 1300 ° C. is necessary, so the manufacturing cost has to be extremely high, and in recent years the manufacturing cost has been reduced. He left a problem where he was unable to meet the demand.

  In order to solve the above problems, for example, in Patent Document 4, 0.010 to 0.060% of acid-soluble Al (sol. Al) is contained, slab heating is suppressed to a low temperature, and nitriding is performed in an appropriate nitriding atmosphere in a decarburization annealing process. Thus, a method has been proposed in which (Al, Si) N is precipitated during secondary recrystallization and used as an inhibitor. (Al, Si) N functions as an effective inhibitor by being finely dispersed in the steel. However, since the inhibitor strength is determined by the Al content, it is sufficient when the Al quantitative accuracy in steelmaking is not sufficient. In some cases, grain growth inhibitory power could not be obtained. Numerous methods have been proposed in which nitriding is performed in the middle of the process and (Al, Si) N or AlN is used as an inhibitor. Recently, a manufacturing method in which the slab heating temperature exceeds 1300 ° C. has also been disclosed. .

On the other hand, a technique for allowing secondary recrystallization to develop without containing an inhibitor component in the slab has been studied. For example, in Patent Document 5, a technique capable of performing secondary recrystallization without containing an inhibitor component, a so-called inhibitor. The less method was developed. This inhibitorless method is a technology that uses secondary steel with higher purity and develops secondary recrystallization by texture (control of texture).
This inhibitor-less method does not require high-temperature slab heating and enables production of grain-oriented electrical steel sheets at a low cost. However, because it does not have an inhibitor, it is affected by temperature variations during the production process. As a result, the magnetic characteristics of the products were also subject to variations. Control of texture is an important element in the present technology, and many techniques such as warm rolling have been proposed for texture control. However, when such texture control cannot be performed sufficiently, the degree of integration in the Goth orientation ((110) [001]) after secondary recrystallization is low and the magnetic flux density tends to be lower than in the technique using an inhibitor. It was in.

U.S. Patent No. 1965559 Japanese Patent Publication No.40-15644 Japanese Patent Publication No.51-13469 Japanese Patent No. 2782086 JP 2000-129356 JP

  As described above, it has not always been easy to stably achieve good magnetic properties in the method of manufacturing grain-oriented electrical steel sheets using the inhibitorless method that has been proposed so far.

The present invention uses a component in accordance with an inhibitorless component in which Al is suppressed to less than 100 ppm, avoids high-temperature slab heating, and precipitates silicon nitride (Si ₃ N ₄ ) instead of AlN by nitriding. The inhibitory effect and the effect of improving the primary recrystallization texture by the combined addition of P and Sb improve the ability to suppress normal grain growth, thereby greatly reducing the variation in magnetic properties and making it industrially stable. This makes it possible to manufacture grain-oriented electrical steel sheets having good magnetic properties.

  In order to obtain a grain-oriented electrical steel sheet with reduced variation in magnetic properties while suppressing the slab heating temperature, the inventors made a primary recrystallized texture using an inhibitorless method, A study was made to deposit silicon nitride using nitriding and to use it as an inhibitor.

  In other words, the inventors control the amount of nitriding during nitriding treatment if silicon that is generally contained in the grain-oriented electrical steel sheet by several percent is precipitated as silicon nitride and can be used as an inhibitor. Therefore, it was thought that the same grain growth inhibiting power could be obtained regardless of the amount of nitride forming elements (Al, Ti, Cr, V, etc.).

  On the other hand, pure silicon nitride, unlike (Al, Si) N, in which Si is dissolved in AlN, has poor consistency between the steel and the crystal lattice, and has a complex crystal structure with covalent bonds. It is known that it is extremely difficult to make it finely precipitate inside. Therefore, it is considered difficult to finely precipitate in the grains after nitriding as in the conventional method.

  However, if this is used in reverse, there is a possibility that silicon nitride can be selectively deposited at the grain boundaries. And if it can be made to precipitate selectively in a grain boundary, it will be thought that sufficient inhibitory force is obtained even if the precipitate is coarse.

  In addition to the above-described inhibitory effect of silicon nitride, the inventors can further improve the grain growth inhibiting power by improving the primary recrystallization texture by utilizing P, which is a grain boundary segregation element. I thought that.

Therefore, the inventors based on the above-mentioned idea, including the composition of the material, the amount of nitrogen after nitriding, the heat treatment conditions for diffusing nitrogen into the grain boundary to form silicon nitride, and further P The intensive study was conducted on the addition conditions and other production conditions.
As a result, adding an appropriate amount of P together with Sb, controlling the cold rolling conditions, and applying a nitriding treatment to obtain a predetermined amount of N is extremely effective in achieving the intended purpose. That is why the present invention has been completed.

That is, the gist configuration of the present invention is as follows.
1. In mass%, C: 0.08% or less, Si: 2.0-4.5% and Mn: 0.5% or less, S, Se and O are each suppressed to less than 50 ppm, sol.Al is suppressed to less than 100 ppm, and N is further reduced. [sol.Al] × (14/27) ppm ≦ N ≦ 80ppm, the remainder is hot-rolled with or without reheating the steel slab with the composition of Fe and inevitable impurities After forming a hot-rolled sheet by annealing and cold rolling to obtain a cold-rolled sheet with the final thickness, followed by primary recrystallization annealing, after applying an annealing separator, secondary recrystallization annealing In the method of manufacturing a grain-oriented electrical steel sheet,
The steel slab further contains, in mass%, Sb and P in a range of 0.01% ≦ Sb ≦ 0.50% and 0.1 × [Sb]% ≦ P ≦ 2.0 × [Sb]%, respectively.
Controlling the temperature in the final cold rolling of the cold rolling in the range of 150 to 250 ° C. and the reduction ratio in the range of 84 to 92%,
After the cold rolling, before the start of secondary recrystallization annealing, performing a nitriding treatment in which the nitrogen amount is 50 ppm or more and 1000 ppm or less,
The above nitriding treatment is performed in a NH ₃ gas or NH ₃ -N ₂ mixed gas atmosphere at a gas temperature of 500 to 800 ° C and a treatment time of 10 to 300 s, or a salt bath of NaCN-Na ₂ CO ₃ -NaCl system. Salt bath temperature by 400 to 600 ° C., treatment time: 30 to 600 s salt bath nitriding, and
Securing a residence time in the temperature range of 300 to 800 ° C. for 5 hours or more in the temperature raising process of the secondary recrystallization annealing,
A method for producing a grain-oriented electrical steel sheet characterized by the above.

2 . The steel slab is further mass%,
Ni: 0.005-1.50%, Sn: 0.01-0.50%,
Cu: 0.01 to 0.50%, Cr: 0.01 to 1.50%,
Mo: 0.01-0.50% and Nb: 0.0005-0.0100%
2. The method for producing a grain-oriented electrical steel sheet according to 1, wherein the composition contains one or more selected from among the above.

According to the present invention, it is possible to industrially stably produce a grain-oriented electrical steel sheet having good magnetic properties by greatly reducing variations in magnetic properties without the need for high-temperature slab heating.
Further, in the present invention, pure silicon nitride that is not complex precipitation with Al is used. Therefore, in the purification, the purification of the steel can be achieved only by purifying only relatively fast-diffusing nitrogen.
Furthermore, when using conventional Al or Ti as precipitates, control in the ppm order was necessary from the viewpoint of final purification and reliable inhibitor effect, but as in the present invention. When Si is used as a precipitate, no such control is necessary during steelmaking.

The magnetic flux density B ₈ (T), is a diagram showing the relationship between the content of P and Sb.

Hereinafter, the present invention will be specifically described.
First, the reason why the component composition of the steel slab is limited to the above range in the present invention will be described. Unless otherwise specified, “%” in relation to ingredients means mass%.
C: 0.08% or less C is an element useful for improving the primary recrystallized texture. However, if the content exceeds 0.08%, the primary recrystallized texture is deteriorated, so the C content is 0.08%. Limited to: A desirable content from the viewpoint of magnetic properties is in the range of 0.01 to 0.06%. If the required magnetic property level is not so high, the C content may be 0.01% or less in order to omit or simplify the decarburization in the primary recrystallization annealing.

Si: 2.0-4.5%
Si is a useful element that improves iron loss by increasing electrical resistance. However, if the content exceeds 4.5%, the cold rolling property deteriorates significantly, so the Si content is limited to 4.5% or less. On the other hand, since Si needs to function as a nitride-forming element, it is necessary to contain 2.0% or more. Further, from the viewpoint of iron loss, the desirable content is in the range of 2.0 to 4.5%.

Mn: 0.5% or less
Mn has the effect of improving hot workability at the time of manufacture, so it is preferable to contain 0.03% or more. However, if the content exceeds 0.5%, the primary recrystallization texture deteriorates and the magnetic properties Therefore, the Mn content is limited to 0.5% or less.

S, Se, and O: each less than 50 ppm When the amounts of S, Se, and O are each 50 ppm or more, secondary recrystallization becomes difficult. This is because coarse oxides and MnS and MnSe coarsened by slab heating make the primary recrystallized structure non-uniform. Accordingly, S, Se, and O are all suppressed to less than 50 ppm.

sol.Al: less than 100ppm
Al forms a dense oxide film on the surface, making it difficult to control the amount of nitridation during nitridation and inhibiting decarburization. Therefore, Al is suppressed to less than 100 ppm as the amount of sol.Al. However, Al with high oxygen affinity is less than 100 ppm (preferably 20 ppm or more) because it can be expected to reduce the amount of dissolved oxygen in the steel by adding a small amount in the steelmaking process and reduce oxide inclusions that lead to property deterioration. ) Can be suppressed by adding in the range of.

[sol.Al] × (14/27) ppm ≦ N ≦ 80ppm
Since the present invention is characterized by precipitating silicon nitride after nitriding, it is important to previously contain N in excess of the N amount necessary for precipitation as AlN with respect to the amount of Al contained. . That is, since AlN is bonded at a ratio of 1: 1, by adding N of [sol.Al] × N atomic weight (14) / Al atomic weight (27) or more, a small amount of Al contained in the steel. Can be completely deposited before nitriding. On the other hand, since N may cause defects such as blisters during slab heating, the N amount needs to be suppressed to 80 ppm or less. Desirably, it is 60 ppm or less.

In addition, in the present invention, in order to improve the primary recrystallization texture and improve the grain growth suppressing power, it is extremely important to contain P and Sb in the following ranges in addition to the above components, respectively. It is.
0.1 × [Sb]% ≦ P ≦ 2.0 × [Sb]%
P is a grain boundary segregation element, and functions to increase Goth orientation in the primary recrystallization texture by suppressing recrystallization nucleation from the grain boundary and promoting recrystallization nucleation from within the grain. is there. In addition, it has the effect of stabilizing the secondary recrystallization nucleation and improving the magnetic properties. In order to effectively exhibit such an effect of improving the primary recrystallization texture accompanying the addition of P, it is important to adjust the P content to an appropriate range according to the Sb content described later.
Here, in order to acquire said effect, it is necessary to contain P 0.1 time or more of Sb amount. On the other hand, if the P content exceeds 2.0 times the Sb content, excessive nitridation and oxidation during secondary recrystallization annealing will occur, or cold rollability will deteriorate. Therefore, P is included in the following range in relation to the amount of Sb.
0.1 × [Sb]% ≦ P ≦ 2.0 × [Sb]%

0.01% ≦ Sb ≦ 0.50%
Sb is a surface segregation element and has the function of stabilizing the expression of secondary recrystallization by optimizing the amount of nitridation and oxidation during secondary recrystallization annealing. In particular, secondary recrystallization annealing by adding P It works to alleviate excessive promotion of nitriding and oxidation at times. For that purpose, it is necessary to contain 0.01% or more of Sb. On the other hand, when the Sb content exceeds 0.50%, the cold rollability deteriorates. For this reason, Sb was included in the range of 0.01 to 0.50%. Preferably it is 0.03 to 0.10% of range.

Here, the experimental results that serve as the basis for controlling the contents of P and Sb within the above ranges will be described.
C: 0.03%, Si: 3.3%, Mn: 0.07%, S: 0.002%, Al: 0.006% and N: 0.0035%, and P and Sb are respectively P: 0 to 0.6%, Sb: 0 to A steel slab containing 0.1% in various ranges with the balance being Fe and inevitable impurities is heated at 1200 ° C for 30 minutes and hot rolled to a 2.2 mm thick hot-rolled sheet at 1055 ° C, 1 After annealing for a minute, cold rolling was performed at a final cold rolling temperature of 200 ° C to obtain a final thickness of 0.22 mm (90% reduction), and the resulting cold rolled coil A 100 mm × 400 mm size sample was taken from the center of the steel and annealed in the lab for both primary recrystallization and decarburization. Subsequently, nitriding treatment was performed at 750 ° C. for 30 minutes in a mixed atmosphere of NH ₃ : 30 vol% and N ₂ : 70 vol%. Note that the amount of N after nitriding was in the range of 200 to 300 ppm.

Thereafter, an annealing separator containing MgO as a main component and containing 5% of TiO ₂ is made into a water slurry, coated and dried, baked on a steel plate, and then a residence time in a temperature range of 300 to 800 ° C. is 30 hours, 800 A final finish annealing was performed under the condition that the temperature range of ˜1200 ° C. was raised in 24 hours, and then a phosphate insulating tension coating was applied and baked to obtain a product.
With respect to the obtained product, the magnetic flux density B ₈ (T) at a magnetizing force of 800 A / m was measured. FIG. 1 shows the relationship between the measured magnetic flux density B ₈ (T) and the contents of P and Sb.

FIG. 1 shows that when only P is contained without containing Sb, the effect of improving the magnetic flux density is not seen, but rather the magnetic flux density is lowered. On the other hand, when P is contained in addition to Sb, when the P content is less than half of the Sb content, that is, when the P content is 2.0 × [Sb]% or less, the magnetic flux density is improved. It can be seen that when the P content is less than 0.1 times the Sb content, that is, when the P content is less than 0.1 × [Sb]%, the magnetic flux density decreases.
From this result, by controlling P and Sb within a predetermined range, the primary recrystallization texture is improved, which contributes to the improvement of the grain growth inhibiting force, and more excellent magnetic properties can be obtained. It became clear.

Although the basic components have been described above, in the present invention, the following elements can be appropriately contained as components that improve the magnetic characteristics more stably industrially.
Ni: 0.005-1.50%
Ni improves the magnetic properties by increasing the uniformity of the hot-rolled sheet structure. For this purpose, Ni is preferably contained in an amount of 0.005% or more. On the other hand, if the content exceeds 1.50%, secondary re-generation is performed. Since it becomes difficult to crystallize and the magnetic properties deteriorate, it is desirable to contain Ni in the range of 0.005 to 1.50%.

Sn: 0.01-0.50%
Sn is a useful element that suppresses nitriding and oxidation of steel sheets during secondary recrystallization annealing and promotes secondary recrystallization of grains having good crystal orientation to improve magnetic properties. However, if it exceeds 0.50%, the cold rolling property deteriorates, so it is desirable to contain Sn in the range of 0.01 to 0.50%.

Cu: 0.01 to 0.50%
Cu suppresses oxidation of the steel sheet during secondary recrystallization annealing, promotes secondary recrystallization of grains having a good crystal orientation, and effectively improves magnetic properties. However, if it exceeds 0.50%, hot rollability deteriorates, so Cu is desirably contained in the range of 0.01 to 0.50%.

Cr: 0.01 to 1.50%
Cr has a function of stabilizing the formation of the forsterite film. For this purpose, it is preferable to contain 0.01% or more. On the other hand, if the content exceeds 1.50%, secondary recrystallization becomes difficult and the magnetic properties are reduced. Since it deteriorates, it is desirable to contain Cr in the range of 0.01 to 1.50%.

Mo: 0.01-0.50%, Nb: 0.0005-0.0100%
Both Mo and Nb have an effect of suppressing the sag after hot rolling through suppression of cracking due to temperature change during slab heating. In these cases, if Mo is not contained in an amount of 0.01% or more and Nb is not contained in an amount of 0.0005% or more, the effect of suppressing the shaving is small. On the other hand, if Mo exceeds 0.50%, Nb exceeds 0.0100%, carbide and nitride are formed. In order to cause deterioration of the iron loss when the final product remains, it is desirable that each be in the above range.

Next, the manufacturing method of this invention is demonstrated.
The steel slab adjusted to the above preferred component composition range is subjected to hot rolling without being reheated or after being reheated. When the slab is reheated, the reheating temperature is desirably about 1000 ° C. or higher and about 1300 ° C. or lower. This is because slab heating above 1300 ° C is meaningless in the present invention, which contains almost no inhibitor in the steel at the slab stage, and only increases the cost, while below 1000 ° C, the rolling load increases. It is because it becomes high and rolling becomes difficult.

Next, the hot-rolled sheet is subjected to hot-rolled sheet annealing as necessary, and then subjected to one cold rolling or two or more cold rollings sandwiching the intermediate annealing to obtain a final cold-rolled sheet.
Here, in the present invention, in order to enhance the segregation effect of P and improve the primary recrystallization texture, it is important to increase the temperature in the final cold rolling of cold rolling to 150 to 250 ° C. Preferably it is the range of 180-220 degreeC.
The appropriate rolling reduction is 84 to 92%. This is because if the rolling reduction is less than 84%, the effect of improving the primary recrystallization texture is not sufficient, while if it exceeds 92%, the secondary recrystallization becomes unstable.

Next, primary recrystallization annealing is applied to the final cold rolled sheet.
The purpose of this primary recrystallization annealing is to adjust the primary recrystallization grain size optimal for secondary recrystallization by primary recrystallization of a cold rolled sheet having a rolled structure. For that purpose, it is desirable that the annealing temperature of the primary recrystallization annealing is 800 ° C. or more and less than 950 ° C. Further, the annealing atmosphere at this time may be a dehumidifying annealing by making the atmosphere of wet hydrogen nitrogen or wet hydrogen argon.

In the present invention, nitriding is performed after the above-described cold rolling and before the start of secondary recrystallization annealing. The nitriding method is not particularly limited as long as the amount of nitriding can be controlled. For example, gas nitridation may be performed using NH ₃ atmosphere gas in the form of a coil, which has been implemented in the past, or nitriding may be continuously performed on a running strip. In this case, preferable processing conditions are a processing temperature: 500 to 800 ° C. and a processing time: 10 to 300 s.
It is also possible to use a salt bath nitriding treatment having a higher nitriding ability than gas nitriding. Here, as the salt bath, a NaCN—Na ₂ CO ₃ —NaCl salt bath is suitable. In this case, preferable treatment conditions are a salt bath temperature: 400 to 600 ° C. and a treatment time: 30 to 600 s.

An important point in the above nitriding treatment is to form a nitride layer on the surface layer. In order to suppress diffusion into the steel, it is desirable to perform nitriding treatment at a temperature of 800 ° C or less. A physical layer can be formed.
Here, the nitrogen amount after nitriding needs to be 50 ppm or more and 1000 ppm or less. If the amount of nitrogen is less than 50 ppm, the effect cannot be sufficiently obtained. On the other hand, if the amount exceeds 1000 ppm, the amount of silicon nitride deposited becomes excessive and secondary recrystallization hardly occurs. Preferably it is the range of 200 ppm or more and less than 1000 ppm.

After performing the above-mentioned primary recrystallization annealing and nitriding treatment, an annealing separator is applied to the steel sheet surface. In order to form a forsterite film on the surface of a steel sheet after secondary recrystallization annealing, it is necessary to use magnesia (MgO) as the main ingredient of the annealing separator, but if it is not necessary to form a forsterite film, annealing is performed. As the separating agent main agent, an appropriate oxide having a melting point higher than the secondary recrystallization annealing temperature, such as alumina (Al ₂ O ₃ ) or calcia (CaO), can be used.

This is followed by secondary recrystallization annealing. In this secondary recrystallization annealing, it is preferable that the residence time in the temperature range of 300 to 800 ° C. is 5 hours or more during the temperature raising step. During this time, the nitride layer mainly composed of Fe ₂ N and Fe ₄ N in the surface layer formed by nitriding is decomposed, and N diffuses into the steel. In the component system of the present invention, since Al that can form AlN does not remain, N as a grain boundary segregation element diffuses into the steel using the grain boundary as a diffusion path.

Since silicon nitride has poor compatibility with steel (high misfit rate), the deposition rate is extremely slow. Nonetheless, since the purpose of precipitation of silicon nitride is to suppress normal grain growth, it is necessary to selectively deposit a sufficient amount on the grain boundary at the 800 ° C stage where normal grain growth proceeds. . In this regard, by setting the residence time in the temperature range of 300 to 800 ° C. to 5 hours or more, silicon nitride cannot be precipitated in the grains, but in combination with N that has diffused the grain boundaries, It can be selectively deposited on the grain boundaries. The upper limit of the residence time is not necessarily provided, but since an improvement in effect cannot be expected even if annealing exceeding 150 hours is performed, the upper limit is preferably set to 150 hours. Note that N ₂ , Ar, H ₂ or a mixed gas thereof is suitable for the annealing atmosphere.

  As described above, the amount of Al in the steel is suppressed, excessive N is added to the AlN precipitation, and the above-described steps are performed for a slab that hardly contains an inhibitor component typified by MnS or MnSe. In the grain-oriented electrical steel sheet manufactured through the process, during the temperature rise process of secondary recrystallization annealing, silicon nitride of coarser size (100 nm or more) than the conventional inhibitor is used as the grain boundary at the stage until the start of secondary recrystallization. It can be formed selectively.

The point of using pure silicon nitride that is not a complex precipitation with Al, which is a feature of the present invention, exists in the order of several percent in steel, and effectively uses Si that has an effect on iron loss improvement. Has very high stability. In other words, components such as Al and Ti that have been used in conventional technology have high affinity with nitrogen and are stable precipitates up to high temperatures, so they are likely to remain in steel and eventually remain in steel. This may cause a deterioration in magnetic characteristics.
However, when silicon nitride is used, it is possible to achieve purification of precipitates that are detrimental to magnetic properties by purifying only nitrogen that is relatively fast diffused. In addition, for Al and Ti, control in the ppm order is necessary from the viewpoint that it must be finally purified, and from the viewpoint that the inhibitor effect must be obtained reliably, but when using Si It is also an important feature of the present invention that such control is unnecessary during steelmaking.

Next, a secondary recrystallization annealing is performed at a temperature of about 850 ° C., and then a purification annealing is performed at a temperature of about 1200 ° C.
Thereafter, an insulating coating can be further applied and baked on the surface of the steel sheet. The type of the insulating coating is not particularly limited, and any conventionally known insulating coating is suitable. For example, a coating solution containing phosphate-chromate-colloidal silica described in JP-A-50-79442 and JP-A-48-39338 is applied to a steel plate and baked at about 800 ° C. The method is preferred.
Further, the shape of the steel sheet can be adjusted by flattening annealing, and this flattening annealing can be combined with the baking treatment of the insulating coating.

Example 1
Contains C: 0.03%, Si: 3.4%, Mn: 0.07%, S: 0.002%, Al: 0.005%, N: 0.003%, P: 0.02% and Sb: 0.05%, the balance being Fe and inevitable impurities A steel slab having the following composition is heated at 1220 ° C for 30 minutes, hot rolled to a hot rolled sheet of 2.2mm thickness, annealed at 1065 ° C for 1 minute, and then cold rolled under the conditions shown in Table 1. Then, a final thickness was obtained, and then a sample of 100 mm × 400 mm size was taken from the center of the obtained cold-rolled coil and annealed in the laboratory for both primary recrystallization and decarburization. Subsequently, nitriding by gas treatment or salt bath treatment was performed under the conditions shown in Table 1 to increase the amount of nitrogen in the steel.

As the nitriding conditions for the gas treatment, a mixed atmosphere of NH ₃ : 30 vol% and N ₂ 70 vol% was used.
As the nitriding conditions for the salt bath treatment, a molten salt of NaCN—Na ₂ CO ₃ —NaCl was used.
After the above nitriding treatment, the N amount of the steel sheet was measured.

Thereafter, an annealing separator containing MgO as a main component and containing 5% of TiO ₂ is made into a water slurry, coated and dried, baked on a steel plate, and then a residence time in a temperature range of 300 to 800 ° C. is 30 hours, 800 A final finish annealing was performed under the condition that the temperature range of ˜1200 ° C. was raised in 24 hours, and then a phosphate insulating tension coating was applied and baked to obtain a product.
The obtained product was evaluated for magnetic flux density B ₈ (T) at a magnetizing force of 800 A / m.

  As shown in Table 1, all of the inventive examples have improved magnetic properties as compared with those manufactured in the conventional inhibitorless manufacturing process.

(Example 2)
A steel slab containing the components shown in Table 2 is heated at 1215 ° C. for 20 minutes, then hot rolled into a 2.4 mm thick hot-rolled sheet, annealed at 1065 ° C. for 1 minute, and then the temperature in the final cold rolling is 250. The final thickness of 0.27mm (rolling rate: 88.8%) was obtained by cold rolling at ℃, and then the annealing temperature was 840 ℃ under the atmosphere of P (H ₂ O) / P (H ₂ ) = 0.3 The decarburization annealing which hold | maintains for 2 minutes on these conditions was performed. Then, 20 seconds of the gas nitriding treatment at 750 ° C. for some coils _{(NH 3: 30vol% + N} 2: under 70 vol% atmosphere) After performing was measured N content of the steel sheet.
Next, an annealing separator containing MgO as the main component and 10% TiO ₂ added is mixed with water to form a slurry, and then wound on a coil, and the residence time between 300-800 ° C is 30 hours. , Final finish annealing is performed in the temperature range of 800-1200 ° C in 24 hours, followed by a flattening annealing for the purpose of applying and baking phosphate-based insulation tension coating and flattening the steel strip. Product.
Table 2 shows the results obtained by collecting the Epstein test piece from the product coil thus obtained and measuring the magnetic flux density B ₈ .

  As is apparent from Table 2, it can be seen that all the inventive examples obtained according to the present invention have a high magnetic flux density.

(Example 3)
A steel slab containing the components shown in Table 3 is heated at 1235 ° C. for 30 minutes, then hot rolled into a hot-rolled sheet having a thickness of 2.0 mm, annealed at 1025 ° C. for 1 minute, and then the temperature in the final cold rolling is 250. ° C. and the cold sheet thickness by rolling: 0.23 mm (rolling reduction 88.5%) after the final thickness _{of, P (H 2 O) /} P (H 2) = 0.35 atmosphere at an annealing temperature of: 850 ° C. and The decarburization annealing which hold | maintains for 2 minutes on these conditions was performed. Thereafter, gas nitriding treatment was performed at 780 ° C. for 20 seconds (NH ₃ : 30 vol% + N ₂ : 70 vol% atmosphere), and then the N amount of the steel sheet was measured.
Next, an annealing separator containing MgO as a main component and adding 5% of TiO ₂ was mixed with water to form a slurry, which was then wound around a coil and the residence time between 300-800 ° C. is shown in Table 3. The final finish annealing was performed under the conditions shown in FIG. 5 and the temperature range of 800 to 1200 ° C. was raised in 24 hours, and the product was subsequently coated and baked with a phosphate-based insulating tension coating.
Table 3 shows the results obtained by collecting an Epstein test piece from the product coil thus obtained and measuring the magnetic flux density B ₈ .

  As can be seen from Table 3, all of the inventive examples obtained according to the present invention have a high magnetic flux density. In particular, No. 1 to 3 in which the residence time in the temperature range of 300 to 800 ° C. was secured for 5 hours or more in the temperature raising process of the secondary recrystallization annealing was No. in which the residence time in the temperature range was less than 5 hours. Compared with .4, higher magnetic flux density is obtained.

Claims (2)

In mass%, C: 0.08% or less, Si: 2.0-4.5% and Mn: 0.5% or less, S, Se and O are each suppressed to less than 50 ppm, sol.Al is suppressed to less than 100 ppm, and N is further reduced. [sol.Al] × (14/27) ppm ≦ N ≦ 80ppm, the remainder is hot-rolled with or without reheating the steel slab with the composition of Fe and inevitable impurities After forming a hot-rolled sheet by annealing and cold rolling to obtain a cold-rolled sheet with the final thickness, followed by primary recrystallization annealing, after applying an annealing separator, secondary recrystallization annealing In the method of manufacturing a grain-oriented electrical steel sheet,
The steel slab further contains, in mass%, Sb and P in a range of 0.01% ≦ Sb ≦ 0.50% and 0.1 × [Sb]% ≦ P ≦ 2.0 × [Sb]%, respectively.
Controlling the temperature in the final cold rolling of the cold rolling in the range of 150 to 250 ° C. and the reduction ratio in the range of 84 to 92%,
After the cold rolling, before the start of secondary recrystallization annealing, performing a nitriding treatment in which the nitrogen amount is 50 ppm or more and 1000 ppm or less,
The above nitriding treatment is performed in a NH ₃ gas or NH ₃ -N ₂ mixed gas atmosphere at a gas temperature of 500 to 800 ° C and a treatment time of 10 to 300 s, or a salt bath of NaCN-Na ₂ CO ₃ -NaCl system. Salt bath temperature by 400 to 600 ° C., treatment time: 30 to 600 s salt bath nitriding, and
Securing a residence time in the temperature range of 300 to 800 ° C. for 5 hours or more in the temperature raising process of the secondary recrystallization annealing,
A method for producing a grain-oriented electrical steel sheet characterized by the above. The steel slab is further mass%,
Ni: 0.005-1.50%, Sn: 0.01-0.50%,
Cu: 0.01 to 0.50%, Cr: 0.01 to 1.50%,
Mo: 0.01-0.50% and Nb: 0.0005-0.0100%
The method for producing a grain-oriented electrical steel sheet according to claim 1, wherein the composition contains one or more selected from among the above.

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